Hello Phil OBrien
Good day to you and thank you for your post in the Microsoft community.
I am truly sorry for the inconvenience this issue has caused you. Based on the description, I understand your concern regarding scheduling meeting interval in increment of 40 minutes. It is a great suggestion to have machine learning mechanisms that would recognizing the daily patterns people use to schedule meeting and suggest 40 minutes instead of 30 minutes or 1 hour. For now, this can be achieved in Microsoft Bookings if you Set up a shared booking page but students will need to book according to your availability.
We do understand your concern about this feature that how it helps you to improve your efficiency in such daily busy work schedule but as it is related with Teams Calendar product design, so it is strongly recommended to submit your valuable feedback directly to Microsoft product development team by either go to Help from your dedicated App > submit Feedback or by posting on Ideas · Community (microsoft.com) for feature requests.
Please note that nobody here are the product developers/decision makers and has no control over the product. Everyone, including us as community moderator, can only assist you on the query for providing available solutions and feature's availability status within our scope and capability.
To check more details about how to submit feedback, kindly refer this article Learn about how to provide feedback to Microsoft - Microsoft 365 admin | Microsoft Learn.
Your understanding and cooperation are greatly appreciated.
Sincerely,
Roger Shen